a c outlets /shore power /inverter..question

[ed flanagan]

i have AC outlets (work when connected to shore power) but no inverter. if i want to install an inverter in order to have a c available under way/at anchor, how do i preclude the possible conflict between shore power A C and inverter AC if i forget and leave the inverter on while connecting shore power?
...
i gotta believe there is a widget for this, but ain't seen one.
thx